In the processing of integrated circuits, electrical contact is typically made to isolated active device regions formed within a wafer substrate typically comprising monocrystalline silicon. The active device regions are connected by high electrically conductive paths or lines which are fabricated above insulative material which covers the substrate surface. To provide electrical connection between the conductive paths, and active-device regions, an opening in the insulative material is typically provided to enable conductive films to make electrical connection with desired regions. Such openings are typically referred to as contact openings, or simply "contacts".
As transistor-active area dimensions approached one micron in diameter, conventional process parameters resulted in intolerable increased resistance between the active region or area and the conductive layer. One way of reducing such contact resistance is by formation of a metal silicide atop the active area prior to application of conductive material which will partially or fully fill the remaining contact opening and/or other material which will be utilized to form the conductive runner. One common metal silicide material formed is TiSi.sub.x, where "x" is predominantly "2".
Ultimately, an electrically conductive contact-filling material, such as tungsten, would be provided for making electrical connection to the contact with the active area. However, tungsten adheres poorly to titanium silicide. Additionally, it is desirable to prevent intermixing of the contact-filling material with the silicide and underlying silicon. Accordingly, an intervening layer is typically provided to prevent diffusion of the silicon and silicide with the plug-filling metal, and to effectively adhere the plug-filling metal to the underlying substrate. Such material is, accordingly, also electrically conductive and commonly referred to as a "barrier layer" due to its anti-diffusion properties. One material of choice for use as a glue/diffusion barrier layer is titanium nitride. This is an attractive material as a contact diffusion barrier in silicon integrated circuits because it behaves as an impermeable barrier to silicon, and because the activation energy for diffusion of other impurities is very high. Titanium nitride is also chemically thermodynamically very stable, and it has low electrical resistance.
Titanium silicide and titanium nitride can be formed in a number of different manners. One prior art process for forming titanium silicide and titanium nitride barrier contacts comprises first depositing an elemental titanium layer by physical vapor deposition (i.e., sputtering) to within a contact opening over a silicon containing region. Subsequently, the wafer is moved from the physical vapor deposition chamber to a chemical vapor deposition chamber. There, titanium nitride is chemical vapor deposited from an organic titanium containing precursor, such as tetrakisdimethylamido titanium (TDMAT). The wafer is subsequently exposed to suitable annealing conditions to transform titanium at the base of the contact into a titanium silicide. Tungsten or some other conductive material (for example, conductively doped semiconductor materials) is then deposited to fill the remaining contact opening. A planarizing process, such as chemical-mechanical polishing, is then utilized to isolate the conductive plug-filling material within the contact opening.
In another process, titanium is chemical vapor deposited utilizing TiCl.sub.4 and H.sub.2 as precursors at sub-atmospheric pressure, at a temperature of around 635.degree. C., and in the presence of plasma. Deposition under these conditions, principally because of the temperature, will cause the titanium which deposits immediately over the silicon-containing active region to constitute titanium silicide. The titanium overlying insulative material will deposit as elemental titanium. The wafer is then moved from the TiCl.sub.4 deposition chamber to an organic chemical vapor deposition chamber where the above-described TDMAT is utilized to deposit a TiN layer. The processing then continues as otherwise described above.
This invention was principally motivated in addressing problems associated with contact plug formation involving titanium silicide and titanium nitride interface materials between a silicon-containing region and an overlying conductive plug-filling material, such as tungsten. The artisan will, however, appreciate applicability of the invention to any other aspect of semiconductor wafer processing whereby a conductive connection is formed on a substrate between a first region comprising silicon and some second region, with the invention only being limited by the accompanying claims appropriately interpreted in accordance with the Doctrine of Equivalents.